Indexing work piece holders utilized in grinding work pieces to a desired shape necessarily embody movable members to enable the work piece to be either rotated about its axis or tilted in a vertical plane, or preferably both. A high degree of precision is often specified in grinding operations, and the quality of the work is largely dependent upon the integrity of close-fitting movable members, the quality rapidly deteriorating when the movable parts are coated by the fine particulates of the grinding wheel dust incident to the operation.
Work holder damage by abrasive dust has long been recognized, and progress has been made in developing structures less susceptible to, but far from completely free, of such damage. The invention herein describes an indexing fixture in which the deposit of abrasive dust upon its movable parts is made less likely by effectively shielding them by other less affected members of the structure.
The precise rotary setting of any indexing device is fundamentally a matter of selecting a desired angle of the indexing plate between two angularly spaced radii in units of degrees, minutes and seconds, the angle being often determined by the use of measuring blocks of a height equal to the sine of the desired angle.
The matter of indexing the rotary indexing plate precisely through the angle so determined has occasioned the development of a large number of indexing devices differing in structure. Obviously a high degree of accuracy may be realized by the use of closely circumferentially spacing a large number of holes peripherally spaced around the rotary indexing plate, using an indexing pin inserted into one of the holes to engage a measuring member of known height. Some prior art indexing devices are described as having over 300 such holes; it is apparent that any structure requiring the precise locating of each of a large number of indexing holes is an expensive article.